HttpSession in Servlet - Java Training School

HttpSession object is used to identify a user in multiple http requests. A unique session id is given to the user when the first request is intercepted. This id is stored in a request parameter or in a cookie.

How to get HttpSession object

There are two methods in HttpServletRequest interface which can be used to get HttpSession object :

public HttpSession getSession() : Returns the current session associated with this request. If the request does not have a session, It creates a new session.
public HttpSession getSession(boolean create) : Returns the current HttpSession associated with this request. If there is no existing session and parameter create is true, returns a new session.

How to set attribute in session object

public void setAttribute(String name,Object value);

How to get attribute from a session object

String value = (String) session.getAttribute("attName");

Session management using HttpSession

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 
Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Login</title>
</head>
<body>
	<form action="loginServlet" method="post">
		Username:<input type="text" name="userName"/>
		<br/><br/>
		Password:<input type="password" name="password"/>
		<br/><br/> 
		<input type="submit" value="Login"/> 
	</form>  
</body>
</html>

LoginServlet.java

package com.javatrainingschool;
import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

public class LoginServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;

	protected void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		response.setContentType("text/html");
		PrintWriter out = response.getWriter();

		// get parameters from request object.
		String userName = request.getParameter("userName").trim();
		String password = request.getParameter("password").trim();

		// check for null and empty values.

		if (userName.equals("admin") && password.equals("admin")) {
			
			HttpSession session = request.getSession();
			//setting username and password in the session object
			session.setAttribute("userName", userName);
			session.setAttribute("password", password);
			out.println("Logged in successfully.<br/>");
			out.println("Click on the below link to see " + "the values of Username and Password.<br/>");
			out.println("<a href='httpSessionServlet'>" + "Click here</a>");
			out.close();
		} else {
			out.print("Wrong username or password. <br/><br/>");
			RequestDispatcher requestDispatcher = request.getRequestDispatcher("/login.html");
			requestDispatcher.include(request, response);
		}
	}
}

HttpSessionExampleServlet.java

package com.javatrainingschool;
import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

public class HttpSessionExampleServlet extends HttpServlet {

	private static final long serialVersionUID = 1L;

	protected void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		response.setContentType("text/html");
		PrintWriter out = response.getWriter();

		//get parameters from session object.
		HttpSession session = request.getSession(false);
		String userName = (String) session.getAttribute("userName");
		String password = (String) session.getAttribute("password");

		out.println("Username: " + userName + "<br/><br/>");
		out.println("Password: " + password);

		out.close();
	}
}

web.xml

<web-app>  
  
    <servlet>  
        <servlet-class>com.javatrainingschool.LoginServlet</servlet-class>  
        <servlet-name>loginServlet</servlet-name>  
    </servlet>  
  
    <servlet-mapping>  
        <servlet-name>loginServlet</servlet-name>  
        <url-pattern>/loginServlet</url-pattern>  
    </servlet-mapping>  
  
    <servlet>  
        <servlet-class>com.javatrainingschool.HttpSessionExampleServlet</servlet-class> 
        <servlet-name>httpSessionServlet</servlet-name>  
    </servlet>  
  
    <servlet-mapping>  
        <servlet-name>httpSessionServlet</servlet-name>  
        <url-pattern>/httpSessionServlet</url-pattern>  
    </servlet-mapping>  
  
</web-app>

Test the application